Ports: only need to when you're sitting behind a router, I believe. go to your router's site (you can usually accesss it by typing 192.168.0.1 in your browser as the URL) and then see what you can find there about opening/forwarding IP adresses. You'll have to see if the example program needs UPD or TCP protocoll.
how to know the IP: http://www.whatismyip.com/ it says it right there, that is still the fastest way of finding your own IP. You usuually only need to open ports if you're the server, so the other PC won#t need to. So it may be easier to get someone without a router to host and then you can join that game.

If you'd like to see this example of code in ANet, I could do it.
To answer your questions from above:
can anyone set that up? how long would it take? has anyone ever done it?
-I believe I can, yes. No promises though.
-between half a day and half a year. Hard to tell. But I'd say, including testing (with you), about 2 days.
-I have, yes. Not with a simple shooter though, we're working on a space action-shooter game which is a little more complex.

So either tell me to do it and I'll try, taking a short break from my game, or you can wait until dark_samurai has finished ANet demos, I think he's working on them. Of course, his demos won't be shooter specific.
If you want to, you can add me on some account (yahoo, ICQ, msn... whatever you have) so it's easier to communicate when we test the thing.